Compare the closed and open controls
The 20 mm cube with one face removed has 10 triangles and four boundary edges; the closed 20 mm cube has 12 triangles, zero boundary edges and screened volume 8,000 mm³ under the millimetre assumption. The open control's volume is unavailable, not zero. These are owned geometry controls with retained local algorithm observations; they are not a new production-endpoint observation.
The missing-face control shows the boundary around a known absent square. In an unknown model, a reported boundary still needs a design decision. Closed material walls can surround an intended passage without exposed mesh edges. Do not cap that passage merely because it looks open. Use the watertight guide to interpret the opening. Check other supported mesh issues when closure is not the only question, or use the manifold checker for edge-sharing questions.
Read this method alongside the result
Server edge incidence matches exact endpoint coordinates without tolerance welding. Invalid-coordinate and degenerate triangles are excluded; duplicate triangles still contribute. An edge used by one triangle is a boundary; more than two incident faces is a separate over-sharing finding. Components connect through shared vertex coordinates, not necessarily printable connections. This check does not prove vertex-manifoldness or run a spatial intersection test.
A completed zero-boundary result, an exposed boundary and unavailable analysis are distinct outcomes. Volume can be withheld by separate validity gates, including multi-component ambiguity; do not read unavailable volume as an additional failed closure test.
Choose a deliberate correction
If a required surface is missing, restore it through a deliberate source-model or mesh-editing workflow. Supported cleanup removes selected existing triangles; it does not reconstruct a missing face. Reopen the saved copy and inspect both topology and affected slicer layers.